In recent years, the practice of treating images as digital data has rapidly increased, along with enhancement of operation capacity and progress in networking technology. Image information of digitized data using a scanner can via computer be readily edited or enhanced with texts or illustrations. Examples of hard copy materials used to prepare a hard copy based on such digitized images include a sublimation type thermal print, a melt type thermal print, an ink-jet print, an electrostatic transfer type print, a thermo-autochrome print and a silver halide color photographic material. Of these, silver halide color photographic material (hereinafter, also referred to as photographic material) has vastly superior characteristics such as high sensitivity, superior tone, superior image durability and lower cost compared to other print materials, and therefore is broadly employed for preparation of high quality hard copy prints.
Digitized image information can be readily manipulated on a computer, leading to increased practice of treating images comprised of a mixture of images based on photography of people, landscapes, still-life and the like (hereinafter, also denoted as scenic images) and text images (specifically, small thin black text). Accordingly, simultaneous distinct reproduction of natural scene with accompanying text reproduction is required of image output based on digital data.
Further, recently high definition output image input devices such as digital cameras or film scanners, has been dramatic, which provides high quality image data for image prints, high definition output devices (such as digital exposure apparatuses). Various types of digital exposure apparatuses performing exposure based on digitized image data are now widely available and many kinds of digital exposure apparatuses have also been developed, along with progress in exposure light sources and exposure control devices. Of these digital exposure apparatuses, these using a narrow wavelength distribution light source, such as lasers or LEDs, have become the mainstay.
However, the kinds of laser or LED installed in various types of digital exposure apparatuses are rather haphazard and the exposure wavelengths and exposure times often differ in most exposure devices. Further, exposure time of digital exposure devices is quite different from that of the former analog exposure through a negative film, resulting in exposure time of 10−7–10−2 seconds, meaning that the difference between the digital and analog exposure ranges at a factor of 10,000–100,000. Therefore, color photographic materials are required to exhibit great latitude in exposure time. Further, due to the nature of the apparatus, such digital exposure devices are very vulnerable to the effects of heat, therefore, at least adequate resistance to heat and humidity during exposure of the color photographic material is essential, compared to the film material for analog exposure. Further, along with ubiquity of mini-labs, there are shops providing print service of less than 35 minutes from receipt of an order to delivery of prints, resulting in incentive for the market to further shorten the processing time, and simultaneously, to provide excellent images, specifically using digital devices. However, techniques to realize digital exposure adequacy of the photographic material exhibit drawbacks of production stability of the silver halide color photographic material, or the techniques adversely affect processing stability of the material during ever faster processing targets.
To overcome the above drawbacks, various proposals to define constitution or characteristic values of the silver halide color photographic material have been disclosed, for example, a color photographic material exhibiting excellent adequacy to exposure time, and a broader range of conditions at exposure is proposed (please refer, for example, to Patent Document 1). According to the method described in Patent Document 1, high quality images may also be stably obtained due to changes of exposure time and conditions of temperature and humidity at exposure, however, it has been proved after experimentation that there are still problems of reciprocity law failure, latent image stability, and processing stability variation.
There have been disclosed various methods to control by using a metal complex (hereinafter referred to as metal) to be doped in silver halide particles, for the aforementioned various characteristics. For example, there is proposed a method to improve sensitivity, gradient or a reciprocity law failure characteristic by doping metals each having a different electron-emitting speed (e.g., see Patent Document 2). There is further proposed a method to conduct sensitization processing by using a silver halide emulsion containing highly silver chloride that contains metal aquocomplex (e.g., see Patent Document 3). Further, there is disclosed a method to improve sensitivity, gradient or a reciprocity law failure characteristic by using an aquocomplex iridium having Br ligand or an organic ligand complex (e.g., see Patent Document 4).
Further, in recent years, in addition to the various performances mentioned above, an increase of photographic fogging and deterioration of a white background resulting therefrom which are caused by an influence of natural radiation existing in the natural world when a silver halide color photographic photosensitive material is preserved for a long period of time have become problems, and measures for them are required.
There has been proposed a silver halide color photographic photosensitive material whose fitness for rapid processing has been improved by using plural types of silver halide emulsions with high content of silver chloride and by stipulating a sensitivity difference of each silver halide emulsion and content of metal complex compound (e.g., see Patent Document 5). Further proposed has been a silver halide color photographic photosensitive material whose tendency for rapid processing and digital processing have been improved by using plural types of silver halide emulsions with high content of silver chloride, and by stipulating contents of silver chloride, silver bromide and silver iodide in the silver halide emulsions employed in each image forming layer. (e.g., see Patent Document 6). However, any of the disclosed methods above cannot provide high sensitivity, sufficient gradation, resistance to radioactive rays, and latent image stability. Further, to correspond to a rapid processing in recent years, enhancement of increasing processing stability is required, however, no technical suggestion to achieve the above characteristics is found at all in these Patent Documents.
A technology for higher sensitivity employing a silver halide emulsion containing iridium complex and having a localized layer of iridium (e.g., see Patent Document 7), or a technology for higher sensitivity and for reducing fog by using a silver halide emulsion wherein an amount of metal complex in the surface area is less than that in the inside of the particle (e.g., see Patent Document 8). However, a method to control precisely iridium content in the inside of a particle is not mentioned in any method, and there is no technical suggestion at all, concerning a method having high sensitivity and sufficient gradient and improving resistance to radioactive rays, processing stability and latent image stability.
(Patent Document 1) Unexamined Japanese Patent Application No. (hereinafter, referred to as JP-A) 2003-207874
(Patent Document 2) JP-A 2002-214733
(Patent Document 3) JP-A 2001-356441
(Patent Document 4) JP-A 2002-357879
(Patent Document 5) JP-A 2004-37549
(Patent Document 6) JP-A 2003-295371
(Patent Document 7) JP-A 11-202440
(Patent Document 8) JP-A 2004-45463